Nickel-based active material precursor for lithium secondary battery, method of preparing the same, nickel-based active material for lithium secondary battery produced from the nickel-based active material precursor, and lithium secondary battery having cathode containing the nickel-based active material

ABSTRACT

Provided are a nickel-based active material precursor for a lithium secondary battery including a porous core and a shell on the porous core, the shell having a radial arrangement structure with a higher density than that of the porous core, wherein the nickel-based active material precursor have a size of 9 μm to 14 μm, and the porous core has a volume of about 5% by volume to about 20% by volume based on the total volume of the nickel-based active material precursor; a method of preparing the nickel-based active material precursor; a nickel-based active material produced from the nickel-based active material; and a lithium secondary battery including a cathode containing the nickel-based active material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/462,912, filed May 21, 2019, which is a National Phase patentapplication of International Patent Application NumberPCT/KR2017/014102, filed Dec. 4, 2017, which claims priority to and thebenefit of Korean Patent Application No. 10-2016-0163896, filed Dec. 2,2016, the entire content of all of which is incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to nickel-based active materialprecursors for lithium secondary batteries, methods of preparing thesame, nickel-based active materials for lithium secondary batteriesproduced from the nickel-based active material precursor, and lithiumsecondary batteries including cathodes containing the nickel-basedactive materials.

BACKGROUND ART

With the development of portable electronic devices, communicationdevices, and the like, there is an increasing demand for lithiumsecondary batteries having high energy density.

Lithium nickel manganese cobalt composite oxides, lithium cobalt oxides,and the like have been used as cathode active materials of lithiumsecondary batteries. However, when such cathode active materials areused, cracks occur in primary particle units with repeated charging anddischarging, thereby reducing the long lifespan of lithium secondarybatteries, increasing battery resistance, and failing to satisfy desiredbattery characteristics. Therefore, there is a need to improve thesecharacteristics.

DESCRIPTION OF EMBODIMENTS Technical Problem

Provided is a nickel-based active material precursor for a lithiumsecondary battery having an increased lithium ion utilization rate.

Provided is a method of producing the nickel-based active materialprecursor.

Provided are a nickel-based active material obtained from thenickel-based active material precursor and a lithium secondary batteryincluding a cathode containing the nickel-based active material.

Solution to Problem

According to an aspect of the present disclosure, a nickel-based activematerial precursor for a lithium secondary battery includes a porouscore and a shell having a radial arrangement structure with higherdensity than that of the porous core.

The nickel-based active material precursor has a particle size of about9 μm to about 14 μm, and the porous core has a volume of about 5% byvolume to about 20% by volume based on the total volume of thenickel-based active material precursor.

According to another aspect of the present disclosure, a method ofproducing a nickel-based active material precursor for a lithiumsecondary battery includes:

a first step of forming a porous core by reacting a mixture of acomplexing agent, a pH regulator, and a metal raw material for forming anickel-based active material precursor; and

a second step of forming a shell on the porous core obtained in thefirst step, the shell having a radial arrangement structure with higherdensity than that of the porous core, wherein a supply rate of the metalraw material for forming a nickel-based active material precursor andthe complexing agent in the second step is reduced as compared to thatof the first step.

According to another aspect of the present disclosure, a nickel-basedactive material for a lithium secondary battery is obtained from thenickel-based active material precursor.

According to another aspect of the present disclosure, a lithiumsecondary battery includes a cathode including the nickel-based activematerial for a lithium secondary battery.

Advantageous Effects of Disclosure

A nickel-based active material precursor for a lithium secondary batteryaccording to an embodiment has increased efficiency as a lithiumdiffusion distance is decreased. By using a cathode including anickel-based active material obtained from the nickel-based activematerial precursor, a lithium secondary battery having increaseddischarge capacity and improved charge/discharge efficiency may bemanufactured.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic diagram illustrating a structure of anickel-based active material precursor according to an embodiment.

FIG. 1B is a schematic diagram illustrating shapes of plate particles ofthe nickel-based active material precursor.

FIG. 1C is a diagram for describing the definition of a radialarrangement in a secondary particle of a nickel-based active materialaccording to an embodiment.

FIG. 2 is a schematic diagram illustrating a structure of a lithiumsecondary battery according to an embodiment.

[Reference Numerals] 21: Lithium secondary battery 22: Negativeelectrode 23: Positive electrode 24: Separator 25: Battery case 26: Capassembly

MODE OF DISCLOSURE

Hereinafter, a nickel-based active material precursor for a lithiumsecondary battery, a method of producing the same, a nickel-based activematerial produced from the nickel-based active material precursor, and alithium secondary battery including a cathode containing thenickel-based active material according to an embodiment of the presentdisclosure will be described in detail with reference to theaccompanying drawings.

Hereinafter, a nickel-based active material precursor according to anembodiment of the present disclosure will be described with reference toFIGS. 1A to 1C. FIG. 1A is a schematic diagram illustrating a structureof a nickel-based active material precursor according to an embodiment,FIG. 1B is a schematic diagram illustrating shapes of plate particles ofthe nickel-based active material precursor, and FIG. 1C is a diagram fordescribing the definition of a radial arrangement in a secondaryparticle of a nickel-based active material according to an embodiment.

Referring to FIG. 1A, a nickel-based active material precursor 10according to an embodiment includes a porous core 11 and a shell 12formed on the porous core 11. Here, the nickel-based active materialprecursor 10 may have a particle size of about 9 μm to about 14 μm and avolume of about 5% by volume to about 20% by volume based on the totalvolume of the porous core 11. The shell 12 may have a greater densitythan that of the porous core 11.

The nickel-based active material precursor having a porous structureaccording to an embodiment may prevent a lithium diffusion length fromincreasing with the increase of the particle size, and may also give adensity gradient by controlling density of the porous core 11 to besmaller than that of the shell 12. In this regard, a cathode activematerial produced from the nickel-based active material precursor has aporous layer in the center of particles that have a small volumefraction but increase a lithium diffusion distance. By controlling thesize of the particles that have a large volume but has a little effecton a lithium diffusion distance, the cathode may have a structureadvantageous in facilitating diffusion of lithium into the particlesduring charging and discharging and adsorbing the stress generatedtherein. In addition, because open pores are well developed on a surfaceresulting from the radial arrangement structure of the nickel-basedactive material precursor, an electrolyte may easily permeatetherethrough so as to facilitate diffusion of lithium. In addition,because the porous core of the nickel-based active material precursorhas a radial arrangement structure, stress may be reduced duringcharging and discharging.

The porous core 11 refers to a region of about 30% by length to about70% by length, for example, 60% by length of the total distance from thecenter of the nickel-based compound to the surface of the nickel-basedcompound from the center of the nickel-based compound, or refers to aremaining region a except for a region within 2 μm in thickness from theoutermost periphery.

The porous core 11 may have an irregular porous pore. The term“irregular porous structure” as used herein refers to a structure havingpores of which a size and a shape are not regular and are non-uniform.

The porous core 11 may include plate particles which may non-uniformlybe arranged. Referring to FIG. 1B, a plate particle may have a polygonalnanoplate shape such as a hexagonal plate shape (A), a nanodisc shape(B), and a rectangular parallelpiped shape (C). In FIG. 1B, a thicknesst of the plate particle is smaller than lengths a and b in the planedirection. The length a in the plane direction may be the same orgreater than the length b in the plane direction. A direction in whichthe thickness t of the plate particle is defined is referred to as athickness direction, and a direction including the lengths a and b isreferred to as a plane direction. The plate particles may be arrangedsuch that a thickness plane of the plate particle may be aligned andaligned to the surface of the secondary particles. Here, a crystal planeto which lithium can enter and exit is exposed to the surface of thesecondary particles, and the crystal plane which is a planeperpendicular to the crystal plane (001) of the nickel-based activematerial precursor refers to a thickness plane of the plate particle.The term “plate particle” as used herein refers to a particle having athickness smaller than a length of a longer axis (a plane direction) ofthe plate particle. The length of the longer axis refers to a maximumlength of the widest plane of the plate particle. That is, the plateparticle refers to a structure in which a thickness tin one axialdirection (i.e., a thickness direction) is smaller than a length a ofthe longer axis in the other direction (i.e., a plane direction).

The shell 12 refers to an area b of 30% by length to 50% by length, forexample, 40% by length, from the outermost surface based on a totaldistance from the center to the surface of the nickel-based activematerial precursor or an area within 2 μm from the outermost surface ofthe nickel-based active material precursor.

The shell 12 may include plate particles like the porous core 11 asdescribed above, and the plate particles may have a structure arrangedin a specific direction. For example, the shell 12 may have a radialarrangement structure. As such, when the shell 12 of the nickel-basedactive material precursor has a radial arrangement structure in the samemanner as in the core, the stress during charging and discharging may befurther reduced. The term “radial(ly)” as used herein means that adirection of the thickness t of a plate (i.e., a plane (001) direction)may be arranged in a direction perpendicular to or within ±5° of adirection perpendicular to a direction R toward a center of thesecondary particle as shown in FIG. 1C.

In one embodiment, a volume ratio of the porous core and the shell maybe, for example, in a range of about 1:4 to about 1:20, for example,about 1:4 to about 1:10.

The core of the nickel-based active material precursor according to anembodiment may have a porosity in a range of about 15% to about 30%, andmay have a pore size of about 150 nm to about 1 μm. In addition, theshell of the nickel-based active material precursor according to anembodiment may have a porosity in a range of about 2% to about 5%, andmay have a pore size in a range of about 50 nm to about 148 nm.Throughout the specification, the term “porosity” refers to a ratio ofan area occupied by pores to a total area.

Throughout the specification, the term “size” refers to, when a subjectis a particle, a diameter or an average diameter of the subject, or whena subject is not a particle, the term refers to a length of a longeraxis of the subject.

The nickel-based active material precursor 10 according to an embodimentmay have a specific surface area of 4 m²/g to 8 m²/g. Due to such alarge specific surface area of the nickel-based active materialprecursor 10, diffusion of lithium may be performed more easily.

The nickel-based active material precursor 10 according to an embodimentmay have a maximum diffusion distance of lithium of 5 μm or less, forexample, 2.3 μm to 5 μm. Due to such a short maximum diffusion distanceof lithium, when a cathode including a nickel-based active materialformed from the nickel-based active material precursor is used for alithium secondary battery, a lithium secondary battery with increasedcharging and discharging efficiency and increased capacity may bemanufactured.

A volume of the nickel-based active material precursor including theporous core 11 and the shell 12 is proportional to the square root of 3of a radius of the nickel-based active material precursor (where volumeof sphere=4/3*πr³). That is, the fraction contributing the total volumebecomes smaller toward the center of the sphere. When the nickel-basedactive material precursor is used, the diffusion distance of lithiumduring charging and discharging is equal to the radius of porous core 11and the shell 12.

The core having a small fraction contributing to the volume of thenickel-based active material precursor may be emptied after the heattreatment. As a result, the diffusion distance may be prevented fromincreasing as the particle size increases. The decrease in the overallvolume due to the vacancies of the core of the nickel-based activematerial precursor may be compensated by using a large-particle-sized(large average particle diameter) nickel-based active materialprecursor. In this regard, the increase in pore spaces of thenickel-based active material precursor may be solved by using asmall-particle-sized nickel-based active material precursor incombination.

In one embodiment, the nickel-based active material precursor mayfurther include a nickel-based active material precursor having a sizeof 9 μm to 14 μm (large-particle-sized nickel-based active materialprecursor) and a nickel-based active material precursor having a size of0.1 μm to 8 μm (small-particle-sized nickel-based active materialprecursor).

The size of the small-particle-sized nickel-based active materialprecursor may be, for example, 2.5 μm to 5.0 μm. A weight ratio of thelarge-particle-sized nickel-based active material precursor and thesmall-particle-sized nickel-based active material precursor in a mixturemay be 9:1 to 1:9.

Hereinafter, a method of producing a nickel-based active materialprecursor according to an embodiment will be described.

The method of producing a nickel-based active material precursoraccording to an embodiment includes: a first step of forming a porouscore by reacting a mixture of a complexing agent, a pH regulator, and ametal raw material for forming the nickel-based active materialprecursor; and a second step of forming a shell on the porous coreobtained in the first step, the shell having a radial arrangementstructure with higher density than that of the porous core. Thenickel-based active material precursor produced according to anembodiment may be prepared to have excellent structural stability byappropriately maintaining pores formed by the crystal planes (001) whileminimizing exposure of the crystal planes (001). In addition, the shellof the nickel-based active material precursor may have a radialarrangement structure, and the length of lithium diffusion may beefficiently controlled by this structure.

In the first step and the second step, a reaction temperature may beadjusted within a range of 40° C. to 60° C., a stirring power may beadjusted within a range of 0.1 kW/m³ to 10.0 kW/m³, and a pH may beadjusted within a range of 10 to 12. In addition, in the first step andthe second step, a concentration of ammonia water which is used as thecomplexing agent may be in a range of 0.1 M to 1 M.

In the first step, a porous core may be formed. In detail, thecomplexing agent and the metal raw material for forming the nickel-basedactive material precursor may be supplied and reacted to form a core.

In the nickel-based active material precursor according to anembodiment, the porous core structure may be influenced by the supplyingspeed of the metal raw material, the concentration of the complexingagent, and the pH of the reaction mixture. The pH regulator serves toform a precipitate from the reaction mixture by adjusting the pH of thereaction mixture. Examples of the pH regulator are ammonium hydroxide,sodium hydroxide (NaOH), sodium carbonate (Na₂CO₃), and sodium oxalate(Na₂C₂O₄). As the pH regulator, for example, sodium hydroxide (NaOH) isused. The complexing agent adjusts a reaction rate of forming aprecipitate in coprecipitation reaction, and may be ammonium hydroxide(NH₄OH) (ammonia water), citric acid, and the like. The complexing agentmay be used in any amount commonly used in the art. As the complexingagent, for example, ammonia water is used.

In the first step, the metal raw material may be supplied at a speed of5 L/hr to 15 L/hr, for example, 7 L/hr to 10 L/hr, and the complexingagent may be supplied at a speed of 0.1 L/hr to 5 L/hr, for example, 0.2L/hr to 3.5 L/hr, and for example, 0.5 L/hr to 2 L/hr. In the firststep, the stirring power may be 0.1 kW/m² to 10 kW/m², for example, 2.0kW/m² to 6.0 kW/m², and the concentration of the complexing agent may be0.1 M to 1 M, for example, 0.3 M to 0.6 M. In the first step, thereaction time may be 15 hours to 20 hours, for example, 15 hours to 17hours.

Particles of the product obtained in the first step may have an averageparticle diameter (D50) may be 5 μm to 10 μm, for example, 8.0 μm to 9.5μm, and for example, 8.5 μm to 9.5 μm.

The second step may include forming a shell on the core obtained in thefirst step, the shell having a greater density than that of the core. Indetail, a metal raw material and a complexing agent are added to thereaction product obtained in the first step, and a pH of a reactionmixture was adjusted and then the resultant reaction mixture wasreacted, so as to form a shell having a radial arrangement structurewith a higher density than that of the porous core is formed on theporous core obtained in the first step.

In the second step, the metal raw material for forming the nickel-basedactive material precursor and the complexing agent may be supplied at aspeed reduced as compared with the first step. In one embodiment, therate at which the metal raw material and the complexing agent aresupplied may be reduced to 10% to 40% based on a rate at which the metalraw material and the complexing agent are supplied in the first step. Assuch, through the changes of the rates at which the metal raw materialand the complexing agent are supplied in the first step and the secondstep, respectively, a nickel-based active material precursor having astructure and a size according to an embodiment may be obtained. Inaddition, in the second step, the density of the nickel-based activematerial precursor may be increased by slowing down a speed at which asurface layer is formed, so as to overcome the reduction of the densityof the nickel-based active material precursor due to pores in thecenter.

In the second step, the metal raw material may be supplied at a speed of3 L/hr to 10 L/hr, for example, 5 L/hr to 8 L/hr, and the complexingagent may be supplied at a speed of 0.1 L/hr to 5 L/hr, for example, 0.2L/hr to 3.5 L/hr, and for example, 0.5 L/hr to 1 L/hr. In addition, inthe second step, the stirring power may be 2.5 kW/m² to 4.5 kW/m², theconcentration of the complexing agent may be 0.1 M to 1 M, for example,0.3 M to 0.6 M, and the reaction time may be 5 hours to 7 hours. In thefirst step and the second step, the concentration of the complexingagent is maintained, but the rate at which the metal raw material issupplied decreases.

In the preparation process, as the metal raw material, a metal precursoris used in consideration of the composition of the nickel-based activematerial precursor. The metal raw material may be metal carbonate, metalsulfate, metal nitrate, metal chloride, and the like.

To prepare the compound represented by Formula 1, a manganese precursor,a nickel precursor, and a cobalt precursor may be used as the metal rawmaterial.

The nickel-based active material precursor according to an embodimentmay be a compound represented by Formula 1:

Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)(OH)₂.  [Formula 1]

In Formula 1, M may be an element selected from boron (B), magnesium(Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium(V), tungsten (W), chromium (Cr), iron (Fe), copper (Cu), zirconium(Zr), and aluminum (Al), and x≤(1−x−y−z), y≤(1−x−y−z), 0<x<1, 0≤y<1, and0≤z<1 may be satisfied.

In Formula 1, 0<x≤⅓, 0≤y≤0.5, 0≤z≤0.05, and ⅓≤(1−x−y−z)≤0.95 may besatisfied.

In Formula 1, metal hydroxide may be, for example,Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂, Ni_(0.5)Co_(0.2)Mn_(0.3)(OH)₂,Ni_(1/3)Co_(1/3)Mn_(1/3)(OH)₂, or Ni_(0.8)Co_(0.1)Mn_(0.1)(OH)₂.

In Formula 1, 0<x≤⅓, and for example, 0.1≤x≤⅓, and y may satisfy0≤y≤0.5, for example, 0.05≤y≤0.3, 0≤z≤0.05, or ⅓≤(1−x−y−z)≤0.95. Forexample, in Formula 1, x, y, and z may satisfy ⅓≤(1−x−y−z)≤0.95. In oneor more embodiments, in Formula 1, z may satisfy 0≤z≤0.05, x may satisfy0<x≤⅓, and y may satisfy 0≤y≤⅓. In one or more embodiments, z in Formula1 may be 0. In one or more embodiments, when z in Formula 1 may satisfy0<z≤0.05, M may be Al.

Hereinafter, a method of producing a nickel-based active material byusing the nickel-based active material precursor according to anembodiment will be described.

A lithium precursor and the nickel-based active material precursoraccording to an embodiment are mixed in a certain molar ratio and thensubjected to a low-temperature heat treatment process at 600° C. to 800°C. to prepare a nickel-based active material.

The lithium precursor may be, for example lithium hydroxide, lithiumfluoride, lithium carbonate, or any mixture thereof. A mixing ratio ofthe lithium precursor and the nickel-based active material precursor isadjusted stoichiometrically to prepare a desired nickel-based activematerial.

The mixing may be performed by dry mixing or by using a mixer.

The low-temperature heat treatment is performed in an oxidizing gasatmosphere. The oxidizing gas atmosphere is performed using an oxidizinggas such as oxygen or air, and the oxidizing gas may include, forexample, 10% by volume to 20% by volume of oxygen or air and 80% byvolume to 90% by volume of an inert gas.

The heat treatment may be performed at a temperature where reactions ofthe lithium precursor and the nickel-based active material precursorproceed and a densification temperature or less than the densificationtemperature. In this regard, the densification temperature refers to atemperature at which crystallization is sufficiently performed torealize a charge capacity obtained by an active material.

The heat treatment is performed, for example, at 600° C. to 800° C.,particularly, at 700° C. to 800° C. A heat treatment time may varyaccording to the temperature of the low-temperature heat treatment, andthe like, but may be, for example, in a range of 3 to 10 hours.

When the heat treatment is performed under the above-describedconditions, primary particles of a nickel-based active materialincluding a shell having a radial arrangement structure and a corehaving a irregular porous structure may be prepared. An average particlediameter of the primary particles of the nickel-based active materialmay be in a range of 100 nm to 250 nm in a shorter axis direction. Dueto such an average particle diameter, stress caused by volume changesduring charging and discharging may be suppressed.

Secondary particles of the nickel-based active material may be subjectedto a second heat treatment (high-temperature heat treatment,high-temperature sintering) in an oxidizing gas atmosphere.

The high-temperature heat treatment is performed, for example, at 700°C. to 900° C. A high-temperature heat treatment time may vary accordingto the temperature of the high-temperature heat treatment, and the like,but may be, for example, in a range of 3 to 10 hours.

The nickel-based active material obtained according to the processdescribed above may have, in the same manner as in the nickel-basedactive material precursor, a structure including a porous core and ashell. Here, the nickel-based active material may include a plateparticle, and a longer axis of the plate particle is radially arranged.

In the nickel-based active material according to an embodiment, whenprimary plate particles are radially arranged, the pores exposed onsurfaces therebetween may be toward a central direction, therebyfacilitating diffusion of lithium from the surface. Uniform shrinkingand expanding are possible during intercalation and deintercalation oflithium by the radially arranged primary particles, pores located in the(001) direction, in which particles expand during deintercalation oflithium, buffer the expansion, the probability of occurrence of cracksdecreases during shrinkage and expansion due to small sizes of primaryplate particles, and the probability of occurrence of cracks betweenprimary particles is further reduced during charging and discharging dueto a change in volume changes by pores of the core. Thus, lifespancharacteristics are improved and an increase of resistance issuppressed.

In the nickel-based active material according to an embodiment, the coremay have a pore size of 150 nm to 550 μm, and the shell may have a poressize of less than 150 nm. The core of the nickel-based active materialmay have closed pores, and the shell may have closed pores and/or openpores. Closed pores are difficult to contain an electrolyte, whereasopen pores may contain the electrolyte in the pores of the core.Throughout the specification, a closed pore refers to an independentpore having a closed wall structure without being connected to anotherpore and an open pore refers to a continuous pore having a wallstructure, at least one portion of which is open, and connected to theshell of the particle.

The secondary particle has open pores having a size of less than 150 nmtoward at a central area of the core. In addition, an average particlediameter of the secondary particles of the nickel-based active materialis in a range of 2 μm to 18 μm, for example, 3 μm to 12 μm.

In the high-temperature heat treatment of the primary particles of thenickel-based active material, a hetero-element compound including atleast one selected from zirconium (Zr), titanium (Ti), aluminum (Al),magnesium (Mg), tungsten (W), phosphorus (P), and boron (B) may furtherbe added thereto.

Examples of the hetero-element compound including at least one selectedfrom zirconium (Zr), titanium (Ti), aluminum (Al), magnesium (Mg),tungsten (W), phosphorus (P), and boron (B) may include titanium oxide,zirconium oxide, aluminum oxide, and the like. The hetero-elementcompound may include both of lithium (Li) and a hetero-element. Thehetero-element compound may be, for example, i) an oxide of at least oneselected from zirconium (Zr), titanium (Ti), aluminum (Al), magnesium(Mg), tungsten (W), phosphorus (P), and boron (B) or ii) an oxideincluding lithium and at least one selected from zirconium (Zr),titanium (Ti), aluminum (Al), magnesium (Mg), tungsten (W), phosphorus(P), and boron (B).

The hetero-element compound may be, for example, ZrO₂, Al₂O₃, LiAlO₂,Li₂TiO₃, Li₂ZrO₃, LiBO₃, and Li₃PO₄.

An amount of the compound including the above-described hetero-elementmay be in a range of 0.0005 to 0.01 parts by weight based on 100 partsby weight of the secondary particles of the nickel-based activematerial. The existence and distribution of the oxide including thehetero-element may be identified by Electron Probe Micro-Analysis(EPMA).

When the active material is discharged, a diffusion rate of lithiumdecreases at the end of discharging and large-particle-sized secondaryparticles of the nickel-based active material increase resistance topermeation of lithium into the cores of the secondary particles of thenickel-based active material, and thus discharge capacity decreases incomparison with charge capacity, thereby deteriorating charge/dischargeefficiency. However, in the secondary particle of the nickel-basedactive material according to an example embodiment, the porous corestructure may reduce a diffusion distance to the core and the shellradially aligned toward the surface may facilitate intercalation oflithium into the surface. In addition, due to small-particle-sizedprimary particles of the nickel-based active material, lithium transferpaths may be easily secured among crystal grains. Also, because theprimary particles have small sizes and pores between the primaryparticles buffer volume changes caused during charging and discharging,stress caused by volumes changes during charging and discharged may beminimized.

Regarding the volume ratio and area ratio of the core and the shell inthe nickel-based cathode active material which is cut in a cross-sectionaccording to an embodiment, when an area within about 60% from thecenter of the nickel-based cathode active material is defined as a core,the core may be occupied by 20% by volume to 35% by volume, for example,about 22%, based on the total volume of the nickel-based activematerial.

C-planes of the primary particles of the nickel-based active materialaccording to an embodiment are aligned in the radial direction.

In the nickel-based active material, the amount of Ni is in a range of ⅓to 0.95 mol %, which is greater than that of each of Mn and Co, based onthe total amount of transition metals (Ni, Co, and Mn).

In the nickel-based active material, the amount of Ni is greater thaneach of the other transition metals based on 1 mole of the transitionmetals. By using the nickel-based active material having such a high Nicontent, the degree of lithium diffusion increases, conductivityincreases, and higher capacity may be obtained at the same voltage in alithium secondary battery including a cathode containing thenickel-based active material. However, lifespan characteristics maydeteriorate due to occurrence of cracks.

The nickel-based active material is, for example,LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂, LiNi_(0.5)Co_(0.2)Mn_(0.302),LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂, LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂, orLiNi_(0.85)Co_(0.1)Al_(0.05)O₂.

The overall porosity of the nickel-based active material is in a rangeof 1% to 8%, for example, 1.5% to 7.3%.

A porosity of the outer portion of the nickel-based active material isless than that of the inner portion. Pores exposed on the surfacearranged toward the center, and sizes of the pores are less than 150 nm,for example, in a range of 10 nm to 100 nm when viewed from the surface.The porosity of the inner portion is in a range of 2% to 20%, and aclosed porosity of the outer portion is in a range of 0.1% to 2%. Theterm “closed porosity” refers to a fraction of closed pores (pores intowhich an electrolytic solution cannot permeate) with respect to a totalvolume of pores.

In the nickel-based active material according to an embodiment, theporosity of the inner portion is in a range of 3.3% to 16.5% and theporosity of the outer portion is in a range of 0.3% to 0.7%.

According to another embodiment, a lithium secondary battery including acathode containing the nickel-based active material, an anode, and anelectrolyte interposed therebetween is provided. A method of producingthe lithium secondary battery will be described later.

The electrolyte of the lithium secondary battery according to anembodiment may be a lithium-containing non-aqueous electrolyte, and theelectrolyte of the lithium secondary battery according to an embodimentmay include a separator.

The cathode and the anode are prepared by coating a cathode activematerial layer-forming composition and an anode active materiallayer-forming composition on current collectors and drying the coatedcompositions, respectively.

The cathode active material layer-forming composition is prepared bymixing a cathode active material, a conductive agent, a binder, and asolvent, and the cathode active material according to an exampleembodiment is used as the cathode active material.

The binder, as a component assisting binding of the active material tothe conductive agent and to the current collector, may be added theretoin an amount of 1 to 50 parts by weight based on 100 parts by weight ofa total weight of the cathode active material. Examples of the bindermay include, but are not limited to, polyvinylidene fluoride, polyvinylalcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose,regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene,polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM),sulfonated EPDM, styrene-butadiene rubber, fluoride rubber, and variouscopolymers. An amount of the binder may be in a range of 2 to 5 parts byweight based on 100 parts by weight of the total weight of the cathodeactive material. When the amount of the binder is within the rangeabove, a high binding force of the active material to the currentcollector is obtained.

The conductive agent may be any material that does not cause anychemical change in a battery and has conductivity, without limitation.For example, the conductive agent may be: graphite such as naturalgraphite and artificial graphite; a carbonaceous material such as carbonblack, acetylene black, ketjen black, channel black, furnace black, lampblack, and thermal black; conductive fiber such as carbon fiber andmetal fiber; carbon fluoride; metal powder such as aluminum powder andnickel powder; conductive whisker such as zinc oxide and potassiumtitanate; conductive metal oxide such as titanium oxide; and conductivematerials such as polyphenylene derivatives.

An amount of the conductive agent may be in a range of 2 to 5 parts byweight based on 100 parts by weight of the total weight of the cathodeactive material. When the amount of the conductive agent is within therange above, a finally obtained electrode has excellent conductivity.

Examples of the solvent may include, but are not limited to,N-methylpyrrolidone in any amount commonly used in the art.

The cathode current collector may have a thickness of 3 to 500 μm and beany material having high conductivity and not causing any chemicalchange in a battery without limitation. Examples of the cathode currentcollector may include stainless steel, aluminum, nickel, titanium,heat-treated carbon, or aluminum or stainless-steel surface-treated withcarbon, nickel, titanium, silver, or the like. The current collector mayhave a surface on which irregularities are formed to enhance adhesiveforce of the cathode active material and may be used in any of variousforms including films, sheets, foils, nets, porous structures, foams,and non-woven fabrics.

Separately, an anode active material, a binder, a conductive agent, anda solvent are mixed to prepare an anode active material layer-formingcomposition.

Examples of the anode active material include, but are not limited to, acarbonaceous material such as graphite and carbon, lithium metal, analloy thereof, and a silicon oxide-based material. According to anexample embodiment of the present disclosure, silicon oxide is used.

The binder is added thereto in an amount of 1 to 50 parts by weightbased on 100 parts by weight of a total weight of the anode activematerial. The binder may be the same type as that of the cathode,without limitation.

The conductive agent is used in an amount of 1 to 5 parts by weightbased on 100 parts by weight of the total weight of the anode activematerial. When the amount of the conductive agent is within this range,a finally obtained electrode has excellent conductivity.

The solvent is used in an amount of 1 to 10 parts by weight based on 100parts by weight of the total weight of the anode active material. Whenthe amount of the solvent is within this range, a process of forming ananode active material layer is easily performed.

The conductive agent and the solvent may be the same types as those usedin preparing the cathode.

The anode current collector is generally formed to have a thickness of 3to 500 μm. The anode current collector may be any conductive materialnot causing any chemical change in a battery without limitation.Examples of the anode current collector may include, but are not limitedto, copper, stainless steel, aluminum, nickel, titanium, heat-treatedcarbon, copper or stainless-steel surface-treated with carbon, nickel,titanium, silver, or the like, or an aluminum-cadmium alloy. Inaddition, like the cathode current collector, the anode currentcollector may have a surface on which irregularities are formed toenhance adhesive force of the anode active material and may be used inany of various forms including films, sheets, foils, nets, porousstructures, foams, and non-woven fabrics.

The separator is interposed between the cathode and the anode eachprepared according to the above-described process.

The separator may have a pore diameter of 0.01 μm to 10 μm and athickness of 5 μm to 300 μm. Particularly, examples of the separatorinclude: an olefin-based polymer such as polypropylene and polyethylene;or a sheet or non-woven fabric formed of glass fibers. When a solidelectrolyte such as a polymer is used as the electrolyte, the solidelectrolyte may also serve as a separator.

A lithium salt-containing non-aqueous electrolyte is formed of anon-aqueous electrolytic solution and lithium. A non-aqueous electrolytemay be a non-aqueous electrolytic solution, an organic solidelectrolyte, an inorganic electrolyte, and the like.

Examples of the non-aqueous electrolytic solution may include, but arenot limited to, any aprotic organic solvent such as N-methylpyrrolidinone, propylene carbonate, ethylene carbonate, butylenecarbonate, dimethyl carbonate, diethyl carbonate, gamma-butyro lactone,1,2-dimethoxy ethane, 2-methyl tetrahydrofuran, dimethylsulfoxide,1,3-dioxolane, N,N-formamide, N,N-dimethylformamide, dioxolane,acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoricacid triester, trimethoxy methane, dioxolane derivatives, sulfolane,methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonatederivatives, tetrahydrofuran derivatives, ether, methyl propionate, andethyl propionate.

Examples of the organic solid electrolyte include, but are not limitedto, polyethylene derivatives, polyethylene oxide derivatives,polypropylene oxide derivatives, polyvinyl alcohol, and polyvinylidenefluoride.

Examples of the inorganic solid electrolyte include, but are not limitedto, Li₃N, LiI, Li₅NI₂, Li₃N—LiI—LiOH, Li₂SiS₃, Li₄SiO₄,Li₄SiO₄—LiI—LiOH, and Li₃PO₄—Li₂S—SiS₂.

The lithium salt may be a material easily dissolved in the non-aqueouselectrolyte, for example, but is not limited to, LiCl, LiBr, LiI,LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆,LiAICl₄, CH₃SO₃Li, CF₃SO₃Li, (CF₃SO₂)₂NLi, (FSO₂)₂NLi, lithiumchloroborate, lower aliphatic lithium carboxylate, lithium tetraphenylborate.

FIG. 2 is a cross-sectional view schematically illustrating arepresentative structure of a lithium secondary battery according to anembodiment.

Referring to FIG. 2, a lithium secondary battery 21 includes a cathode23, an anode 22, and a separator 24. The cathode 23, the anode 22, andthe separator 24 are wound or folded, and then accommodated in a batterycase 25. Subsequently, an organic electrolyte is injected into thebattery case 25, and the battery case 25 is sealed with a cap assembly26, thereby completing the manufacture of the lithium secondary battery21. The battery case 25 may have a cylindrical, rectangular, orthin-film shape. For example, the lithium secondary battery 21 may be alarge-particle-sized thin-film battery. The lithium secondary batterymay be a lithium ion battery. The separator is interposed between thecathode and the anode to form a battery assembly. After the batteryassembly is stacked in a bi-cell structure and impregnated with theorganic electrolyte, the obtained resultant is accommodated in a pouch,thereby completing the manufacture of a lithium ion polymer battery. Inaddition, a plurality of battery assemblies may be stacked to form abattery pack, which may be used in any device that requires highcapacity and high output. For example, the battery pack may be used innotebook computers, smart phones, and electric vehicles.

Also, the lithium secondary battery may be used in electric vehicles(EVs) due to excellent storage stability at high temperature, lifespancharacteristics, and high-rate characteristics. For example, the lithiumsecondary battery may be used in hybrid vehicles such as plug-in hybridelectric vehicles (PHEVs).

Hereinafter, the present disclosure will be described in more detailwith reference to the following examples and comparative examples.However, the following examples and comparative examples are merelypresented to exemplify the present disclosure, and the scope of thepresent disclosure is not limited thereto.

Preparation Example 1: Manufacture of Nickel-Based Active MaterialPrecursor

A nickel-based active material precursor (Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂)was synthesized according to a co-precipitation method described below.As a metal raw material forming the nickel-based active materialprecursor in the following manufacturing process, nickel sulfate(NiSO₄.6H₂O), cobalt sulfate (CoSO₄.7H₂O), and manganese sulfate(MnSO₄.H₂O) were used.

First, ammonia water having a concentration of 0.4 mol/L was added to areactor. Reaction was initiated at the stirring power of 3.5 kW/m³ at areaction temperature of 40° C. while a metal raw material and ammoniawater were added at respective speeds of 9 L/hr and 1 L/hr.

Next, NaOH was added to the reactor to maintain the pH. Here, thereactor had pH of 11.0 to 12.0. Within this pH range, the reaction wascontinued for 16 hours. In the first step, forming of a porous core ofthe nickel-based active material precursor was performed.

In the second step, the reaction was carried out in the same manner asin the first step, except that a metal raw material was added to thereaction product obtained in the first step at a speed of 5 L/hr, andammonia water was added thereto at a speed of 0.5 L/hr.

The reaction in the second step was performed for 6 hours, so as to forma shell on the porous core, the shell having a radial arrangementstructure with a higher density than that of the porous core. Here, thepH in the reactor was maintained in the same manner as in the firststep. In the second step, the density of the nickel-based activematerial precursor was increased by slowly controlling a speed at whicha surface layer of the shell was formed, so as to overcome the densityreduction caused by pores of the porous core.

Afterwards, the reaction product obtained in the above processes waswashed, and a postprocess was carried out by washing the reactionresultant and drying the washed resultant in a hot-air dryer at about150° C. for 24 hours, thereby manufacturing a nickel-based activematerial precursor, i.e., metal hydroxide(Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂) having a size of 9 μm.

Preparation Example 2: Manufacture of Nickel-Based Active MaterialPrecursor

A nickel-based active material precursor, i.e., metal hydroxide(Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂) having a size of 14 μm, was manufacturedin the same manner as in Preparation Example 1, except that the stirringpower was reduced to 2.0 kW/m³ to synthesize a precursor having a sizeof 14 μm.

Preparation Example 3: Manufacture of Nickel-Based Active MaterialPrecursor

A nickel-based active material precursor, i.e., metal hydroxide(Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂), was manufactured in the same manner asin Preparation Example 1, except that the manufacturing process waschanged to obtain metal hydroxide (Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂), whichis a nickel-based active material precursor, having a porosity of thecore of about 15% and a porosity of the shell of 3%.

Preparation Example 4: Manufacture of Nickel-Based Active MaterialPrecursor

A nickel-based active material precursor, i.e., metal hydroxide(Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂), was manufactured in the same manner asin Preparation Example 1, except that the amount of ammonia water, thepH, and the stirring power for the metal raw material were changed toobtained metal hydroxide (Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂) which is anickel-based active material precursor having a size of Table 1 below:

TABLE 1 Diameter of Diameter of Thickness of Proportion of Proportion ofcore shell shell shell core (μm) (μm) (μm) (% by volume) (% by volume)4.5 12 3.8 94.7  5.3 5.0 12 3.5 92.8  7.2 5.7 12 3.2 89.3 10.7 6.0 123.0 87.5 12.5 6.3 12 2.9 85.5 14.5 7.0 12 2.5 80.2 19.8

Example 1: Manufacture of Nickel-Based Active Material

The metal hydroxide (Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂) manufacturedaccording to Preparation Example 1 and lithium hydroxide (LiOH) weredry-mixed at a molar ratio of 1:1, and the mixture was heat-treated inan air atmosphere at about 800° C. for 6 hours, thereby obtainingprimary particles of a nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂). The primary particles thus obtained hada core having a porous structure and a shell having a radial arrangementstructure. Through this process, secondary particles of the nickel-basedactive material (LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂) were obtained.

Examples 2 and 3: Manufacture of Nickel-Based Active Materials

Secondary particles of the nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂) were obtained in the same manner as inExample 1, except that the nickel-based active material precursorsrespectively of Preparation Examples 2 and 3 were respectively usedinstead of the nickel-based active material precursor of PreparationExample 1.

Comparative Preparation Example 1: Manufacture of Nickel-Based ActiveMaterial Precursor

A nickel-based active material precursor (Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂)were obtained in the same manner as in Preparation Example 1, exceptthat the metal raw material and the ammonia water in the first step weresupplied at respective speeds of 6.5 L/hr and 0.8 L/hr, and that themetal raw material and the ammonia water in the second step weresupplied at respective speeds of 8.5 L/hr and 1.0 L/hr.

The speeds at which the metal raw material and the ammonia water weresupplied in the second step were increased in comparison with the speedsof the metal raw material and the ammonia water were supplied in thefirst step.

When performed according to Comparative Preparation Example 1, it isdifficult to obtain a nickel-based active material precursor having asize and a structure according to an embodiment.

Comparative Preparation Example 2: Manufacture of Nickel-Based ActiveMaterial Precursor

A nickel-based active material precursor, metal hydroxide(Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂), was manufactured in the same manner asin Comparative Preparation Example 1, except that the conditions of amanufacturing process were controlled so as to obtain a nickel-basedactive material precursor, metal hydroxide(Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂), having the size shown in Table 2 below:

TABLE 2 Proportion Proportion Diameter Diameter Thickness of shell ofcore of core of shell of shell (% by (% by (μm) (μm) (μm) volume)volume) Comparative 2.0 12 5.0 99.5 0.5 Preparation 3.0 12 4.5 98.4 1.6Example 2 3.5 12 4.3 97.5 2.5 4.0 12 4.0 96.3 3.7

Comparative Examples 1 and 2: Manufacture of Nickel-Based ActiveMaterials

Primary particles of the nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂) were obtained in the same manner as inExample 1, except that the nickel-based active material precursors ofComparative Preparation Example 1 and Comparative Preparation Example 2were respectively used instead of the nickel-based active materialprecursor of Preparation Example 1.

Manufacture Example 1: Coin Half-Cell

A coin half-cell was prepared according to the following method by usingsecondary particles of the nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂) obtained according to Example 1 as acathode active material.

96 g of the secondary particles of the nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂) obtained according to Example 1, 2 g ofpolyvinylidene fluoride, 47 g of N-methyl pyrrolidone as a solvent, and2 g of carbon black as a conductive agent were mixed using a mixer whileremoving air bubbles therefrom to prepare a uniformly dispersed cathodeactive material layer-forming slurry.

The slurry prepared according to the process was coated on an aluminumfoil by using a doctor blade to form a thin electrode plate. Theelectrode plate was dried at 135° C. for 3 hours or more, followed byrolling and vacuum drying to prepare a cathode.

A 2032 type coin half-cell (coin cell) was prepared by using the cathodeand a lithium metal as a counter electrode. A separator (thickness:about 16 μm) formed of a porous polyethylene (PE) film was interposedbetween the cathode and the lithium metal counter electrode and anelectrolyte was injected thereinto, thereby preparing a 2032 type coinhalf-cell. Here, for used as the electrolyte, a solution containing 1.1MLiPF₆ dissolved in a mixed solution of ethylene carbonate (EC) andethymethyl carbonate (EMC) mixed at a volume ratio of 3:5 was used.

Manufacture Examples 2 and 3: Preparation of Coin Half-Cells

Coin half-cells were prepared in the same manner as in ManufactureExample 1, except that the nickel-based active materials respectivelyprepared according to Examples 2 and 3 were used instead of thesecondary particles of the nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂) of Example 1 in the manufacture of thecathode.

Comparative Manufacture Examples 1 and 2: Preparation of Coin Half-Cells

Coin half-cells were prepared in the same manner as in ManufactureExample 1, except that the nickel-based active materials preparedaccording to Comparative Examples 1 and 2 were used instead of thesecondary particles of the nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂) of Example 1 in the manufacture of thecathode in Example 1.

Evaluation Example 1: Composition Analysis

The nickel-based active materials respectively manufactured according toExample 1 and Comparative Example 1 were evaluated by inductivelycoupled plasma (ICP) analysis, and the results are shown in Table 3below. Accordingly, the nickel-based active materials being evaluatedwere both confirmed to be well controlled and synthesized by targetadjustment.

TABLE 3 Ni Co Mn Example 1 0.610 0.195 0.195 Comparative 0.607 0.1970.196 Example 1

Evaluation Example 2: Specific Surface Area

Specific surface areas of the nickel-based active materials respectivelymanufactured according to Example 1 and Comparative Example 1 weremeasured by the BET method. Here, the specific surface area was obtainedbased on the internal porosity and, and the results are shown in Table 4below:

TABLE 4 Example 1 Comparative Example 1 Specific surface area (m²/g)5.65 2.43

Referring to Table 4, it was confirmed that the specific surface area ofthe nickel-based active material of Example 1 was larger than that ofthe nickel-based active material of Comparative Example 1.

Evaluation Example 3: X-Ray Diffraction (XRD) Analysis

Crystal structures of the nickel-based active material precursorsrespectively manufactured according to Preparation Example 1 andComparative Preparation Example 1 were analyzed by X-ray diffraction(XRD) analysis. The XRD was performed by using an X'pert pro(PANalytical) with Cu Kα radiation (1.54056 Å), and the results areshown in Table 5 below:

TABLE 5 Comparative Preparation Preparation Unit Example 1 Example 1 a3.042 3.044 (Å) c 4.580 4.608 (Å) c/a 1.506 1.514

Referring to Table 5, it was shown that the c-axis value of thenickel-based active material precursor of Preparation Example 1 wasincreased compared with the case of Comparative Preparation Example 1.Accordingly, the nickel-based active material precursor of PreparationExample 1 had the c-axis value of 4.6 Å or more. When this nickel-basedactive material precursor was used for the synthesis of an activematerial, a large passage through which lithium migrates was possiblyprovided as compared with the case of Comparative Example 1.

Evaluation Example 4: Charging and Discharging Characteristics (InitialCharacteristics)

First, each of the coin half-cells prepared according to ManufactureExamples 1 to 3 and Comparative Manufacture Example 1 was charged anddischarged once with 0.1 C for formation, and then, charged anddischarged once with 0.2 C to identify initial charging and dischargingcharacteristics. While repeating the charging/discharging process 50times at 45° C. with 1 C, cycle characteristics were examined. Thecharge process was set to begin in a constant current (CC) mode, beconverted into a constant voltage (CV) mode, and be cut off at 4.3 Vwith 0.05 C, and the discharge process was set to be cut off in a CCmode at 3.0 V.

The initial charging/discharging efficiency was measured, and theresults are shown in Table 6 below:

TABLE 6 Initial charging/discharging efficiency (%) Manufacture Example1 95.2 Manufacture Example 2 94.3 Comparative Manufacture Example 1 90.5

Referring to Table 6, it was confirmed that the coin half-cells preparedaccording to Manufacture Examples 1 and 2 had improvedcharging/discharging efficiency with 1 C as compared with the case ofComparative Manufacture Example 1. In addition, the coin half-cellprepared according to Manufacture Example 3 showed initialcharging/discharging efficiency characteristics equivalent to those ofthe coin half-cell of Manufacture Example 1.

Evaluation Example 5: Charging and Discharging Characteristics (RateCapability)

The rate capability of each of the coin half-cells prepared according toManufacture Examples 1 to 3 and Comparative Manufacture Example 1 wasevaluated according to the following method.

Each of the coin half-cells prepared according to Manufacture Examples 1to 3 and Comparative Manufacture Examples 1 and 2 was charged under theconditions of a constant current (0.2 C) and a constant voltage (4.3 V,0.05 C cut-off), rested for 10 minutes, and discharged under theconditions of a constant current (0.2 C, ⅓ C, 0.5 C, 1 C, 2 C, or 3 C)until the voltage reached 3.0 V. That is, the rate capabilitycharacteristics of each coin half-cell were evaluated by periodicallychanging the discharge rate at 0.2 C, ⅓ C, 0.5 C, 1 C, 2 C, or 3 C whilethe number of charging and discharging cycles increases. However, eachcell was discharged at a rate of 0.1 C during the 1st to 3rd chargingand discharging cycles.

The rate capability of the coin half-cells was defined by Equation 2below, and the representative results of the discharging with 0.2 C and1 C are shown in Table 7 below:

Rate capability characteristics [%]=(Discharge capacity when dischargingcell at predetermined constant current rate)/(Discharge capacity whendischarging cell at 0.1 C rate)×100  <Equation 2>

The results of the rate capability characteristics are shown in Table 7below:

TABLE 7 Rate capability Rate capability (@ 0.2 C/0.1 C) (@ 1.0 C/0.1 C)Manufacture Example 1 99.0 93.9 Comparative Manufacture Example 1 98.290.5 182.1

Referring to Table 7, the coin half-cell prepared according toManufacture Example 1 had improved rate capability as compared with thecoin half-cell prepared according to Comparative Manufacture Example 1.In addition, when compared with Manufacture Example 1, the coinhalf-cells prepared according to Manufacture Examples 2 and 3 wereequivalent thereto.

Evaluation Example 6: High-Temperature Lifespan Characteristics

The lifespan characteristics of the coin half-cells prepared accordingto Preparation Examples 1 to 3 and Comparative Manufacture Example 1were evaluated according to the following method.

Each coin half-cell was charged and discharged once with 0.1 C forformation, and then, charged and discharged once with 0.2 C to identifyinitial charging and discharging characteristics. While repeating thecharge/discharge process 50 times at 45° C. with 1 C, cyclecharacteristics were examined. The charge process was set to begin in aconstant current (CC) mode, be converted into a constant voltage (CV)mode, and be cut off at 4.3 V with 0.05 C, and the discharge process wasset to be cut off in a CC mode at 3.0 V. Changes in discharge capacityaccording to repeated cycles were examined, and the lifespan of the coinhalf cells was calculated according to Equation 3 below and the resultsare shown in Table 8 below:

Lifespan (%)=(Discharge capacity after 50^(th) cycle/Discharge capacityafter 1^(st) cycle)×100  [Equation 3]

TABLE 8 Lifespan (%) Manufacture Example 1 98.9 Manufacture Example 299.5 Comparative Manufacture Example 1 98.3

Referring to Table 8, it was confirmed that the coin half-cells ofManufacture Examples 1 and 2 had improved lifespan characteristics ascompared with the case of Comparative Manufacture Example 1. Inaddition, when compared with Manufacture Example 1, the coin half-cellprepared according to Manufacture Example 3 was equivalent thereto.

Evaluation Example 7: SEM Analysis

Particles of the nickel-based active material precursors manufacturedaccording to Preparation Example 1 and Comparative Preparation Example 1were partially fractured, and cross-sections of the fractured particleswere analyzed using a scanning electron microscope (SEM). In addition,surfaces of the nickel-based active materials obtained from thenickel-based active material precursors and prepared according toExample 1 and Comparative Example 3 were analyzed using an SEM. For useas an SEM, Magellan 400L (FEI company) was used. Cross-sections ofsamples were pre-processed by milling using a CP2 manufactured by JEOLat 6 kV and 150 uA for 4 hours. In addition, the SEM analysis wasperformed under conditions of 350 V and 3.1 pA SE.

As a result of the SEM analysis, it was confirmed that the nickel-basedactive material precursor manufactured according to Preparation Example1 had a crystal plane (001) aligned outward, so that the nickel-basedactive material had pores having a size of 100 nm to 200 nm alignedtoward the center and had a structure in which the plane (001) wasaligned outward. In addition, as a result of examining thecross-sectional structure of the resulting fractured product of thenickel-based active material precursor manufactured according toPreparation Example 1, it was confirmed that the primary particles had aplate structure.

In comparison, it was confirmed that the plane (001) in the nickel-basedactive material precursor manufactured according to ComparativePreparation Example 1 was not aligned from the center to the outside, sothat, unlike the nickel-based active material precursor manufacturedaccording to Preparation Example 1, the nickel-based active materialprecursor manufactured according to Comparative Preparation Example 1was fractured in an irregular manner.

Evaluation Example 9: Maximum Diffusion Distance of Lithium

Regarding the nickel-based active material precursor manufacturedaccording to Preparation Example 4, a thickness of the shell, a volumeof the shell, a volume of the core, and a maximum diffusion distance oflithium were examined, and the results are shown in Table 9 below. Here,the maximum diffusion distance of lithium is the same as the thicknessof the shell, and the diameter of the shell in Table 9 below can beinterpreted to have the same meaning as the size of the nickel-basedactive material.

TABLE 9 Maximum Proportion of Proportion of diffusion Diameter ofDiameter of Thickness of shell (% by core (% by distance of core (μm)shell (μm) shell (μm) volume) volume) lithium (μm) Preparation 4.5 123.8 94.7 5.3 3.8 Example 4 5.0 12 3.5 92.8 7.2 3.5 5.7 12 3.2 89.3 10.73.2 6.0 12 3.0 87.5 12.5 3.0 6.3 12 2.9 85.5 14.5 2.9 7.0 12 2.5 80.219.8 2.5 Comparative 2.0 12 5.0 99.5 0.5 5.1 Preparation 3.0 12 4.5 98.41.6 4.5 Example 2 3.5 12 4.3 97.5 2.5 4.3 4.0 12 4.0 96.3 3.7 4.0

Referring to Table 9, it was confirmed that the nickel-based activematerial precursor manufactured according to Preparation Example 4 had ashort diffusion distance of lithium as compared to the nickel-basedactive material precursor manufactured according to ComparativePreparation Example 2.

Evaluation Example 6: Porosity Analysis

The nickel-based active material precursors manufactured according toPreparation Examples 1 and 3 and the nickel-based active materialprecursor manufactured according to Comparative Preparation Example 1were analyzed using an SEM.

For use as an SEM, Magellan 400L (FEI company) was used. Cross-sectionsof samples were pre-processed by milling using a CP2 manufactured byJEOL at 6 kV and 150 uA for 4 hours. In addition, the SEM analysis wasperformed at 350 V.

The analysis results are shown in Table 10 below.

TABLE 10 Region Porosity (%) Preparation Porous core 29.93 Example 1Shell 4.52 Preparation Porous core 15 Example 3 Shell 3 ComparativePorous core 1.56 Preparation Shell 3.25 Example 1

While one or more exemplary embodiments have been described withreference to the preparation examples and examples, it will beunderstood by those of ordinary skill in the art that various changes inform and details may be made therein without departing from the spiritand scope as defined by the following claims.

What is claimed is:
 1. A nickel-based active material precursor for alithium secondary battery, comprising: a porous core; and a shell havinga radially arranged structure having a higher density than the porouscore, wherein the nickel-based active material precursor has a size ofabout 9 μm to about 14 μm, the porous core has a volume of about 5% byvolume to about 20% by volume based on the total volume of thenickel-based active material precursor, and a maximum diffusion distanceof lithium in the nickel-based active material precursor is 5 μm orless, and a porosity of the porous core is in a range of about 15% toabout 30%.
 2. The nickel-based active material precursor of claim 1,wherein a porosity of the shell is in a range of about 2% to about 5%.3. The nickel-based active material precursor of claim 1, wherein thenickel-based active material precursor comprises a plate particle, and amajor axis of the plate particle is radially arranged.
 4. Thenickel-based active material precursor of claim 1, wherein thenickel-based active material precursor is a compound represented byFormula 1:Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)(OH)₂  [Formula 1] wherein M in Formula 1is an element selected from boron (B), magnesium (Mg), calcium (Ca),strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), tungsten (W),chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum(Al), and x≤(1−x−y−z), y≤(1−x−y−z), z≤(1−x−y−z), 0<x<1, 0≤y<1, and 0≤z<1are satisfied.
 5. The nickel-based active material precursor of claim 4,wherein an amount of nickel in the nickel-based active materialprecursor is ⅓ to 0.95 mol % of the total amount of transition metals(Ni, Co, and Mn), and the amount of nickel is greater than that of Mnand the amount of nickel is greater than that of Co.
 6. The nickel-basedactive material precursor of claim 1, wherein the nickel-based activematerial precursor is Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂,Ni_(0.5)Co_(0.2)Mn_(0.3)(OH)₂, Ni_(1/3)Co_(1/3)Mn_(1/3)(OH)₂,Ni_(0.8)Co_(0.1)Mn_(0.1)(OH)₂, or Ni_(0.85)Co_(0.1)Al_(0.05)(OH)₂.
 7. Anickel-based active material for a lithium secondary battery, obtainedfrom the nickel-based active material precursor of claim
 1. 8. A lithiumsecondary battery comprising: a cathode comprising the nickel-basedactive material of claim 7; an anode; and an electrolyte between thecathode and the anode.
 9. A method of preparing a nickel-based activematerial precursor for a lithium secondary battery, the methodcomprising: performing a first step of forming a porous core by reactinga mixture of a complexing agent, a pH regulator, and a metal rawmaterial for forming a nickel-based active material precursor; andperforming a second step of forming a shell on the porous core of thefirst step, the shell having a radially arranged structure having ahigher density than that of the porous core.
 10. The method of claim 9,wherein a supply rate of the complexing agent and the metal raw materialfor forming a nickel-based active material precursor in the second stepis reduced as compared to that in the first step.